The present invention relates generally to a load lock chamber, and more particularly to a load lock chamber for use with a fabrication process of a semiconductor substrate, a liquid crystal display (“LCD”) plate, etc., which transports an object, such as a semiconductor substrate and an LCD, from a port as a supply part to a process chamber that provides an exposure process etc., and replaces an atmosphere between the ambient pressure and a reduced pressure environment. The present invention is also directed to a processing system having this load lock chamber.
Recent demands for smaller and lower profile electronic apparatuses have increasingly sought for finer semiconductor devices to be mounted onto these electronic apparatuses. A projection exposure apparatus has been conventionally employed which projects a circuit pattern formed on a mask (or a reticle) onto a wafer etc. via a projection optical system to transfer the circuit pattern in the lithography for manufacturing semiconductor devices.
The minimum critical dimension transferable by the projection exposure apparatus or resolution is proportionate to a wavelength of light used for exposure, and inversely proportionate to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the higher the resolution is. Therefore, a shorter wavelength of a recent exposure light source has been promoted from KrF excimer laser (with a wavelength of approximately 248 nm) to ArF excimer laser (with a wavelength of approximately 193 nm), F2 laser (with a wavelength of approximately 157 nm), and soft X-rays from a synchrotron radiation ring.
Since exposure light with a short wavelength, such as light from an F2 laser and soft X-rays, greatly attenuate in the air, it has been proposed to accommodate an exposure part of an exposure apparatus in a chamber, and to replace the atmosphere in the chamber with nitrogen (N2) and reduced pressure helium (He) which do not cause much attenuation of the exposure light. There are proposed an electron beam exposure apparatus, an EUV exposure apparatus etc. that use a vacuum atmosphere. A processing apparatus, such as a CVD apparatus, often replaces an inner atmosphere with a gas atmosphere different from the air and a vacuum atmosphere for prevent the resist on a substrate from oxidizing or for the process gas different from the air.
FIG. 6 is a schematic block diagram of a conventional processing system 1000. FIG. 7 is a schematic block diagram of a detailed structure of the conventional processing system 1000. Referring to FIGS. 6 and 7, the conventional processing system 1000 typically includes a load lock chamber 1400 that delivers a wafer, such as a semiconductor substrate and a LCD plate, between a port 1200 as a supply part and a process chamber 1100 that provides an exposure process etc., and replaces an atmosphere between the ambient pressure and a reduced pressure environment.
A first transport means 1300 picks up one wafer from a wafer carrier 1222 on a wafer carrier holder chuck 1210, and delivers the wafer to the load lock chamber 1400. When the wafer is carried to the load lock chamber 1400 and placed on a wafer holder chuck 1410, a first gate valve 1420 closes for disconnection from the air, and the atmosphere in the load lock chamber 1400 is replaced. A description will now be given of a replacement of the atmosphere in the load lock chamber 1400.
When the first and second gate valves 1420 and 1430 close for disconnections of the load lock chamber 1400 from the air and the process chamber 1100, an exhaust valve 1520 opens and a vacuum pump (not shown) exhausts the load lock chamber 1400. After the load lock chamber 1400 is exhausted to the predetermined degree of vacuum, the exhaust valve 1520 closes and stops vacuum-pumping.
Then, a He gas supply valve 1620 opens to supply He gas to the load lock chamber 1400 from a He gas supply unit (not shown) through a He gas pipe 1610. The load lock chamber 1400 includes a N2 gas supply valve 1720 in addition to the He gas supply valve 1620. Since the He gas supply valve 1620 supplies gas for the (reduced He) atmosphere in the process chamber 1100 that accommodates the exposure part, the load lock chamber 1400 opens the He gas supply valve 1620 to supply He gas until the load lock chamber 1400 and the process chamber 1100 have the same pressure.
When they have the same pressure, the He gas supply valve 1620 closes and stops supplying the He gas, and ends a replacement of the atmosphere in the load lock chamber 1400.
Subsequent to the replacement of the atmosphere in the load lock chamber 1400, the second gate valve 1430 opens and a second transport means 1800 in the process chamber 1100 takes out the wafer and delivers it to the exposure part accommodated in the process chamber 1100. The wafer exposed by the exposure part is returned to the wafer carrier 1220 via the load lock chamber 1400 by the first and second transport means 1300 and 1400.
There are time limits defined by the following Equation 1, where the processing system 1000 has the throughput of 60 sheets per hour, there are two load lock chambers 1400 for improved throughput, each acting in the same way, “a” [s] is a wafer transport time of the first transport means 1300, “b” [s] is a wafer transport time of the second transport means 1800, “c” [s] is an atmosphere replacement time (from the air to He) in the load lock chamber 1400, and “d” [s] is an atmosphere replacement time (from He to the air) in the load lock chamber 1400:a×2+b×2+c+d<60[s]×2  (1)
If the wafer transport time “a” [s] of the first transport means 1300 and the wafer transport time “b” [s] of the second transport means 1800 are each 10 [s], then the replacement time of the atmosphere in the load lock chamber 1400 is totally 80 [s]. When it is assumed that it takes about 10 [s] to introduce He gas and it takes about 15 [s] to introduce the air, the time limits are not met unless the air is exhausted in 30 [s] and the He atmosphere is exhausted in 25 [s]. In replacing the atmosphere in the load lock chamber 1400 (from He to the air), the air may be merely introduced in 60 [s] without an exhaustion of He gas.
A replacement of the load lock chamber with a vacuum atmosphere has two significant problems: Firstly, while the gas is being exhausted from the load lock chamber, the gas's temperature drop due to the adiabatic expansion cools a wafer that contacts gas. The wafer's temperature drop exceeds its temperature stability budget required in the exposure.
The other problem is adhesions of particles to the wafer. More specifically, the exhaustion blows particles up in exchanging an atmosphere in the load lock chamber, causing them to adhere to the wafer. It is also pointed out that the gas's temperature drop below the dew point due to the adiabatic expansion separates out moisture in the gas, causing the moisture to adhere to the wafer with neighboring fine particles when the moisture coagulates. Disadvantageously, the particles adhered wafer does not accept high-quality processes.
Accordingly, conventional methods have proposed to slow vacuum-pumping at the inception of the exhaustion, and to supply gas simultaneous with the exhaustion (see, for example, Japanese Patent Applications, Publication Nos. 6-318536 and 9-85076). These methods reduce initial exhaust amounts, whereby the retarded exhaustion mitigates the gas flow and restrains particles' blowing up.
In addition, the long exhaust time extends the heat exchange time between the process chamber and the gas, and gas's temperature drop. During the exhaustion, the gas's temperature drops due to the adiabatic expansion. However, indeed the gas contacts walls of the load lock chamber, receives heat, and does not exhibit a complete adiabatic expansion. As the exhaust time becomes long, the contact time with the walls of the load lock chamber becomes long, the gas receives more heat through heat exchanges with the process chamber, and the gas's temperature drop amount reduces.
However, the slow exhaustion naturally delays a completion of exhaustion. The throughput is an important exposure factor necessary for one wafer, and the long exhaust time in the load lock chamber lowers the throughput. In other words, the above methods do not sufficiently take care of the throughput deterioration.
While the above time limits are to maintain the throughput and to replace the atmosphere in the load lock chamber, the time periods, such as maximum 60 [s] for a replacement of the atmosphere in the load lock chamber, which includes 25 [s] to 30 [s] for an gas exhaustion and 10 to 15 [s] for a gas supply, are not sufficient for disadvantageous particles' blowing up and gas's temperature drop.